The present invention relates to a process of manufacturing a wet laid fibrous veil suitable for the preparation of reinforced articles. The wet laid fibrous veils comprise microspheres, which improve the rigidity or impact resistance of the reinforced articles and particularly, lightweight articles.
Microspheres have been incorporated into fibrous nonwoven reinforcements, which are useful in the production of molded composite articles to provide for the formation of lightweight composites. It has been found that the use of expanded microspheres results in a considerable savings of resin and glass fiber in dry-laid fibrous webs. Additionally, the mechanical properties of the product reinforced with the web, such as rigidity or impact resistance, are at least maintained, or even improved, and the thermal insulation capacity is enhanced.
For example, UK Patent No. 1,427,647 and U.S. Pat. No. 3,676,288 describe the application to, or incorporation of non-expanded microspheres into a fibrous web using a binder, such as a polyacrylonitrile latex. As the binder resin is dried and cross-linked, the microspheres are attached to the fibrous web and expanded. In U.S. Pat. No. 4,818,583, a method of manufacturing a bonded fibrous web comprising microspheres were described. However, these methods of adding the microspheres to the fibrous web were directed to a dry-laid process.
Fibrous webs or veils, which are one form of fibrous nonwoven reinforcements, are extremely suitable as reinforcements for many kinds of cured synthetic plastic materials, such as polyester or epoxy resin. Fibrous veils are typically made by a dry or wet-laid process. Typically, glass and mineral fibers have been integrated into the fibrous veils to provide added strength and durability to the composite article made by molding the veil. However, the use of glass fibers in a dry-laid process wears out the machines typically involved in the dry-laid process. Accordingly, integrating glass fibers in a dry-laid process may be costly.
There is a thus a need for a wet-laid process of making fibrous veils that can be used as a reinforcement in composite molding, which allows for the cost-effective incorporation of glass or other reinforcement and allows for the incorporation of microspheres for added rigidity and impact resistance. Furthermore, there is a need to obtain a continuous and efficient method of producing such fibrous reinforcements.
A method of making a microsphere-filled wet-laid veil is disclosed. In one embodiment, the method comprises forming a non-woven fibrous veil, and impregnating microspheres into the veil to form a microsphere-filled wet-laid veil. Preferably, the step of impregnating microspheres into the veil is achieved by contacting the veil with an impregnation binder composition comprising a binder and the microspheres. In a preferred embodiment, the method comprises forming a pre-bonded veil of glass fibers without microspheres. Subsequently, the pre-bonded veil is impregnated inline with a binder composition comprising a binder and microspheres, then the microspheres are expanded.
The invention further comprises microsphere-filled wet-laid veils produced according to the above-mentioned method. Moreover, the invention comprises molded composite articles made using the wet-laid veils manufactured according to the present invention.